It's commercially driven, making sure domestic, international and transit passengers share a common usage lounge means there has to be some check to prevent anyone swapping tickets and a transit passenger with no right to enter the UK boarding a domestic and getting off without clearing passport control. (Transit passengers are not subject to immigration controls unlike the US).
Rather than insist we all carry passports, they stop you at security and take your picture, however this is another barrier to progress, forgivable at a large hub but dumb at MAN where thousands of people every day are subject to it for the benefit of a handful, literally a smidgen of Intl-Intl transit passengers.
Thanks for the explanation,
Skipness One Echo, makes sense! and certainly preferable to the tiresome alternative of carrying passports on a domestic flight.
Haven't found it a hardship at LHR because the photo is taken at points where pax are already checked: (1) at the entrance to security where boarding passes are checked, and (2) at the gate where boarding passes are again checked and pax are hanging around waiting to be called to board the aircraft.
Previously to the Biometric face scanners being introduced, any Intl-Intl pax were escorted to the gate by a security agent and were handed over to the Dispatcher/Gate staff. - A much more sensible approach for the small number of Intl-Intl transfer pax.
Certainly better than the American way of dealing with international-international connections. However, an airport like MAN or BHX, with aspirations to be a hub and to have more than just a smidgen of international-international connections, it was inevitable that this system would need to be installed.